AM79C970 datasheet(111/168 Pages) AMD

111 / 168 page

AMD

P R E L I M I N A R Y

1-978

Am79C970

port when the PORTSEL bits of

the

Mode

(CSR15)

have selected 10BASE-T as the

active port.

When ASEL is set to a ZERO,

then the selected network port

will be determined by the settings

of the PORTSEL bits of CSR15.

The ASEL bit is reset to ONE by

H_RESET and is unaffected by

S_RESET or STOP.

The network port configurations

are as follows:

PORTSEL

ASEL

LINK Status

Network

CSR15[1:0]

(BCR2[1])

(of 10BASE-T)

Port

0 X

Fail

AUI

0 X

Pass

10BASE-T

0 0

AUI

0 1

10BASE-T

1 0

Reserved

1 1

Reserved

XMAUSEL

Reserved location. The default

value of this bit is a ZERO. Writ-

ing a ONE to this bit has no effect

on the operation of the device.

Existing drivers may write a ONE

to this bit, but new drivers should

write a ZERO to this bit.

BCR4: Link Status LED (LNKST)

Bit

Name

Description

BCR4 controls the function(s)

that the

LNKST pin displays.

Multiple functions can be simul-

taneously enabled on this LED

pin. The LED display will indicate

the logical OR of the enabled

functions. BCR4 defaults to Link

Status

(LNKST)

with

pulse

stretcher enabled (PSE = 1) and

is fully programmable.

The default setting after H_RE-

SET for the LNKST register is

00C0h.

The

LNKST

value is unaffected by S_RESET

or STOP.

31–16

RES

Reserved locations. Written as

ZEROs and read as undefined.

LEDOUT

This bit indicates the current

(non-stretched) value of the LED

output pin. A value of ONE in this

bit indicates that the OR of the

enabled signals is true.

The logical value of the LEDOUT

status signal is determined by the

settings of the individual Status

Enable bits of the LED register

(Bits 6–0).

This bit is READ only by the host,

and is unaffected by H_RESET,

S_RESET or STOP.

LEDPOL

LED Polarity. When this bit has

the value ZERO, then the LED

pin will be driven to a LOW level

whenever the OR of the enabled

signals is true and the LED pin

will be disabled and allowed to

float high whenever the OR of the

enabled signals is false. (i.e. the

LED output will be an Open Drain

output and the output value will

be the inverse of the LEDOUT

status bit.)

When this bit has the value ONE,

then the LED pin will be driven to

a HIGH level whenever the OR of

the enabled signals is true and

the LED pin will be driven to a

LOW level whenever the OR of

the enabled signals is false. (i.e.

the LED output will be a Totem

Pole output and the output value

will be the same polarity as the

LEDOUT status bit.)

The setting of this bit will not af-

fect the polarity of the LEDOUT

bit for this register.

LEDDIS

LED Disable. This bit is used to

disable the LED output. When

LEDDIS has the value ONE, then

the LED output will always be

floated. When LEDDIS has the

value ZERO, then the LED out-

put value will be governed by the

LEDOUT and LEDPOL values.

12–8

RES

Reserved locations. Write as ZE-

ROS, read as undefined.

A value of 0 disables the signal.

A value of 1 enables the signal.

PSE

Pulse Stretcher Enable. Extends

the LED illumination time for

each new occurrence of the en-

abled function for this LED

output.

A value of 0 disables the function.

A value of 1 enables the function.

LNKSTE

Link Status Enable. Indicates the

current link status on the Twisted

Pair interface. When this bit is set

to one, a value of ONE will be

passed to the LEDOUT signal to

indicate that the link status state

is PASS. A value of ZERO will be

passed to the LEDOUT signal to

indicate that the link status state

is FAIL.

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